Either I have completely misunderstood your question or you misunderstand the nature of localStorage.You seem to think that localStorage is a direct mechanism for making form data permanent. Maybe you should research the subject further.

The user fills in a field, and presses Submit, and the data is saved to local storage. clearData() is used to clear all the user's entries. So my question is how to clear only the one entry of one field?

The user fills in a field, and presses Submit, and the data is saved to local storage. clearData() is used to clear all the user's entries. So my question is how to clear only the one entry of one field?

localStorage.removeItem([I]<font color='"#696969"'>key</font>[/I]) // to remove an item from local storage.
localStorage.addItem([I]<font color='"#696969"'>key</font>[/I], [I]<font color='"#696969"'>value</font>[/I]) // to add an item to local storage.

The page that you referred to earlier uses a shortcut to add an item, which is: